Millions of people take statin drugs to lower their cholesterol. But the medications may also interfere with the positive effects of exercise in some patients, according to a small study published in the Journal of the American College of Cardiology.

Obese and overweight adults on the cholesterol-lowering drug simvastatin saw less fitness improvement than others not taking statins, University of Missouri researchers found. Simvastatin is a generic type of statin, previously sold under the brand name Zocor.

In the study, 37 previously sedentary and obese people walked or jogged on a treadmill for 12 weeks; 18 of them also took 40 milligrams of simvastatin daily.

After 12 weeks, those in the exercise-only group increased their cardiorespiratory fitness by an average of 10 percent. Those who exercised and took statins saw a 1.5 percent increase.

Those in the exercise-only group also showed an increase in “skeletal muscle mitochondrial content,” a normal response to exercise that improves the muscles’ ability to use energy. The simvastin group showed a decrease in mitochondrial content.

The exercise-only group did not receive a placebo – which could have contributed to the outcome. But the researchers cited other studies that suggested “statins can cause undesirable effects on skeletal muscle mitochondrial function,” and said in light of the mounting evidence, the placebo effect was unlikely.

People at risk for heart disease or metabolic syndrome often are prescribed statins to lower their blood cholesterol; at the same time, they’re advised to exercise more. Both statins and exercise have been independently proven to lower cardiovascular disease risk. But as the study suggested, they may not pair well.

Outside observers say the finding is in line with what some patients on statins report after starting an exercise program. “Some say they feel a change in exercise tolerance,” said preventive cardiologist Stephen Devries, executive director of the non-profit Gaples Institute for Integrative Cardiology, who was not involved in the study. “For high-risk people, there does seem to be an overall advantage in taking a statin. But it may come with a cost – so let’s not put statins in the drinking water.”

To learn more about cholesterol, nutrition and other heart-related issues, attend the upcoming Trib U workshop "A Healthy Heart" which I'll be cohosting with Dr. Devries. The class, held from 6 to 8 p.m Thursday at the Tribune Tower, will explain how nutrition can fight heart disease, why consumers need to be supplement savvy and how to find evidence-based health advice. Here’s how to order tickets.